Question

我有一堆UIViews的课程。一些符合特定协议。我有一些这些特殊的数组，但是我不能在这个数组上调用index（of :)（这段代码可以粘贴到Playground中）：

import UIKit

protocol ViewWithColor {}

class BlackView: UIView {}
class WhiteView: UIView {}
class BlueView: UIView, ViewWithColor {}
class GreenView: UIView, ViewWithColor {}
class YellowView: UIView, ViewWithColor {}

let blackView = BlackView()
let whiteView = WhiteView()
let blueView = BlueView()
let greenView = GreenView()
let yellowView = YellowView()

let allViews = [blackView, whiteView, blueView, greenView, yellowView]
let viewsWithColorArray: [ViewWithColor] = [blueView, greenView, yellowView]

let index1 = allViews.index(of: blueView)
let index2 = viewsWithColorArray.index(of: blueView)

错误是：

cannot invoke 'index' with an argument list of type '(of: BlueView)'

无法调用该函数，因为协议ViewWithColor不符合Equatable。我真的必须实现equatable吗？或者有更好的方法吗？

Answer 1

正如@vadian所说，你可以使用需要关闭的index版本。在这种情况下，您正在寻找特定实例，因此请使用index(where: { $0 === blueView })。

===运算符：

返回一个布尔值，指示两个引用是否指向相同的对象实例。

此外，您需要使协议ViewWithColor成为class协议，因为===仅适用于类实例。

protocol ViewWithColor: class {}

class BlackView: UIView {}
class WhiteView: UIView {}
class BlueView: UIView, ViewWithColor {}
class GreenView: UIView, ViewWithColor {}
class YellowView: UIView, ViewWithColor {}

let blackView = BlackView()
let whiteView = WhiteView()
let blueView = BlueView()
let greenView = GreenView()
let yellowView = YellowView()

let allViews = [blackView, whiteView, blueView, greenView, yellowView]
let viewsWithColorArray: [ViewWithColor] = [blueView, greenView, yellowView]

let index1 = allViews.index(where: { $0 === blueView })
print(index1 ?? -1)

let index2 = viewsWithColorArray.index(where: { $0 === blueView })
print(index2 ?? -1)

Answer 2

您可以使用闭包语法并检查类型：

let index1 = allViews.index(where: {$0 is BlueView})
let index2 = viewsWithColorArray.index(where: {$0 is BlueView})

如何使用[SomeProtocol]索引（of :)？

2 个答案: